alpha thalassemia in black populations.

The different alpha thalassemia genotypes in American and Jamaican black populations have been defined by hematologic and globin-chain synthesis studies, alpha/beta globin messenger RNA ratios and restriction endonuclease mapping of DNA. The results indicate that the common form of alpha thalassemia in these populations is the deletion type of alpha-thalassemia 2 (- alpha/alpha alpha). The homozygous state (- alpha/alpha- alpha) is expressed at birth by the presence of more than 2--3% hemoglobin Bart's; in adult life it has the same phenotype as the heterozygous state for the deletion form of alpha-thalassemia 1 (--/alpha alpha). The heterozygous state is not always associated with detectable amounts of hemoglobin Bart's at birth or with recognizable hematologic changes in adults.